Perivascular mechanisms of CGRP-induced migraine symptoms Project Summary Migraine is a debilitating neurological condition involving the neuropeptide calcitonin gene-related peptide (CGRP). It affects 15% of the population and is the second leading cause of years lived with a disability. Indeed, over 40% of women will experience migraine during their lifetime. An exciting development is the recent FDA approval of a new class of CGRP-targeted drugs designed to prevent migraine. However, a critical need remains because these drugs do not work for all patients. To improve the efficacy of CGRP-based drugs and pave the way for new drug development, we need to know more about how CGRP works in migraine. The objective of this project is to identify the mechanisms by which CGRP acts at both peripheral and central sites to trigger migraine-like symptoms. The scientific premise is that migraine involves increased sensitivity to CGRP, which is supported by clinical studies that have shown CGRP is both required and sufficient to cause migraine. During the past funding period, we developed transgenic mice that are sensitized to CGRP actions. The CGRP-sensitized mice have elevated expression of a subunit of the CGRP receptor called human receptor activity-modifying protein 1 (hRAMP1). We found that CGRP causes a migraine-like symptom (photophobia) by distinct, but possibly overlapping actions in the central nervous system (CNS) and periphery. Here we propose to measure migraine-like symptoms in wildtype and hRAMP1 transgenic mice, using light aversion as an indicator of photophobia, and touch sensitivity and grimace as indicators of pain. We hypothesize that CGRP acts at perivascular sites in the dura and thalamus to cause migraine-like symptoms of photophobia and pain. Specifically, we propose that CGRP-induced vasodilation in the periphery alters the trigeminovascular microenvironment, and that centrally it facilitates the action of CGRP as a neuromodulator in the posterior thalamic region. The first aim will test whether peripheral CGRP mechanisms involve actions on blood and lymphatic vessels and resident mast cells in the dura. The second aim will test whether central CGRP mechanisms involve perivascular and neuromodulatory actions in the posterior thalamic nuclei. Complementary genetic and pharmacological strategies will be used in both aims. These studies will provide insight into the mechanisms that enable CGRP to act both centrally and peripherally, via the vasculature, to affect sensory functions in a neurological disorder. Despite advances in our understanding of migraine over the past decade, many questions remain unanswered, in part due to the paucity of appropriate animal models. The use of our novel CGRP-sensitized hRAMP1 mice represents an innovative approach for challenging the current dogma regarding the vascular roles of CGRP in the periphery and brain. The outcome of this proposal will be the uncovering of perivascular CGRP actions in the dura and CNS that induce migraine-like symptoms. Importantly, this will facilitate development of vascular-targeted and CNS-penetrant therapeutics for migraine.